Imaging lens

ABSTRACT

The present invention relates to an imaging lens, the imaging lens including , in an ordered way from an object side, a first lens having positive (+) refractive power, a second lens having negative (−) refractive power, a third lens having positive (+) refractive power, a fourth lens having positive (+) refractive power, and a fifth lens having negative (−) refractive power, wherein an aperture is interposed between the first and second lenses, and the imaging lens meets a conditional expression of 20&lt;V2&lt;30 and 50&lt;V3,V4,V5&lt;60, where Abbe&#39; number of second lens is V2, Abbe&#39;s number of third lens is V3, Abbe&#39;s number of fourth lens is V4, and Abbe&#39;s number of fifth lens is V5.

TECHNICAL FIELD

The teachings in accordance with exemplary embodiments of this inventionrelate generally to an imaging lens.

BACKGROUND ART

Recently, vigorous research efforts are being made in the field of amobile phone-purpose camera module, a digital still camera (DSC), acamcorder, and a PC camera (an imaging device attached to a personcomputer) all connected with an image pick-up system. One of the mostimportant components in order that a camera module related to such animage pickup system obtains an image is an imaging lens producing animage.

Previously, there have been attempts to construct an imaging lens ofhigh-resolution by using 5 pieces of lenses. Each of 5 pieces of lensesis comprised of lenses with a positive (+) refractive power and lenseswith a negative (−) refractive power. For example, an imaging lens isconstructed on a structure of PNNPN (+−−+−), PNPNN (+−+−−) or PPNPN(++−+−) in order starting from an object side. However, an imagingmodule of such a framework fails to show approving optic characteristicsor aberration characteristics. Accordingly, a high-resolution imaginglens of a new power structure is required.

DISCLOSURE OF INVENTION Technical Problem

Accordingly, embodiments of the present invention may relate to animaging lens that substantially obviates one or more of the abovedisadvantages/problems due to limitations and disadvantages of relatedart, and it is an object of the present invention to provide an imaginglens configured to correct aberration and realize a clear image.

Technical problems to be solved by the present invention are notrestricted to the above-mentioned, and any other technical problems notmentioned so far will be clearly appreciated from the followingdescription by skilled in the art.

Solution to Problem

In one general aspect of the present invention, there is provided animaging lens, the imaging lens comprising, in an ordered way from anobject side: a first lens having positive (+) refractive power; a secondlens having negative (−) refractive power; a third lens having positive(+) refractive power; a fourth lens having positive (+) refractivepower; and a fifth lens having negative (−) refractive power, wherein anaperture is interposed between the first and second lenses, and theimaging lens meets a conditional expression of 20<V2<30 and50<V3,V4,V5<60, where Abbe's number of second lens is V2, Abbe's numberof third lens is V3, Abbe's number of fourth lens is V4, and Abbe'snumber of fifth lens is V5.

Preferably, but not necessarily, an object side surface of the firstlens is convexly formed.

Preferably, but not necessarily, the second lens takes a concave form atan upper side surface.

Preferably, but not necessarily, the third, fourth and fifth lensesrespectively take a meniscus form convexly formed at an upper sidesurface.

Preferably, but not necessarily, any one lens or more lenses from thefirst, second, third, fourth and fifth lenses take an aspheric form.

Preferably, but not necessarily, the imaging lens meets a conditionalexpression of 0.5<fl/f<1.5, where f is an entire focus distance of theimaging lens, and fl is a focus distance of the first lens.

Preferably, but not necessarily, the imaging lens meets a conditionalexpression of 0.5<ΣT/f<1.5, where f is an entire focus distance of theimaging lens, and ΣT is a distance from an object side surface of thefirst lens to an image-forming surface.

Preferably, but not necessarily, the imaging lens meets a conditionalexpression of 1.6<N2<1.7, where N2 is a refractive index of the secondlens.

Advantageous Effects of Invention

The imaging lens according to the present invention has advantageouseffects in that flare can be reduced by interposing a separate aperturebetween a first lens and a second lens to correct aberration and torealize a clear image and by constructing the imaging lens with 5 piecesof lenses comprised of first, second, third, fourth and fifth lenses.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a constructional view illustrating a camera module lensaccording to the present invention.

FIG. 2 is a graph measuring coma aberration according to an exemplaryembodiment of the present invention.

FIG. 3 is a graph illustrating an aberration according to an exemplaryembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The following description is not intended to limit the invention to theform disclosed herein. Consequently, variations and modificationscommensurate with the following teachings, and skill and knowledge ofthe relevant art are within the scope of the present invention. Theembodiments described herein are further intended to explain modes knownof practicing the invention and to enable others skilled in the art toutilize the invention in such, or other embodiments and with variousmodifications required by the particular application(s) or use(s) of thepresent invention.

The disclosed embodiments and advantages thereof are best understood byreferring to FIGS. 1-3 of the drawings, like numerals being used forlike and corresponding parts of the various drawings. Other features andadvantages of the disclosed embodiments will be or will become apparentto one of ordinary skill in the art upon examination of the followingfigures and detailed description. It is intended that all suchadditional features and advantages be included within the scope of thedisclosed embodiments, and protected by the accompanying drawings.Further, the illustrated figures are only exemplary and not intended toassert or imply any limitation with regard to the environment,architecture, or process in which different embodiments may beimplemented. Accordingly, the described aspect is intended to embraceall such alterations, modifications, and variations that fall within thescope and novel idea of the present invention.

It will be understood that the terms “includes” and/or “including” whenused in this specification, specify the presence of stated features,regions, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof. That is, the terms “including”, “includes”, “having”,“has”, “with”, or variants thereof are used in the detailed descriptionand/or the claims to denote non-exhaustive inclusion in a manner similarto the term “comprising”.

Furthermore, “exemplary” is merely meant to mean an example, rather thanthe best. It is also to be appreciated that features, layers and/orelements depicted herein are illustrated with particular dimensionsand/or orientations relative to one another for purposes of simplicityand ease of understanding, and that the actual dimensions and/ororientations may differ substantially from that illustrated. That is, inthe drawings, the size and relative sizes of layers, regions and/orother elements may be exaggerated or reduced for clarity. Like numbersrefer to like elements throughout and explanations that duplicate oneanother will be omitted. Now, the present invention will be described indetail with reference to the accompanying drawings.

Words such as “thus,” “then,” “next,” “therefore”, etc. are not intendedto limit the order of the processes; these words are simply used toguide the reader through the description of the methods.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other elements or intervening elements maybe present. In contrast, when an element is referred to as being“directly connected” or “directly coupled” to another element, there areno intervening elements present.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first region/layer could be termeda second region/layer, and, similarly, a second region/layer could betermed a first region/layer without departing from the teachings of thedisclosure.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the generalinventive concept. As used herein, the singular forms “a”, “an” and“the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise.

Now, the imaging lens according to exemplary embodiments of the presentinvention will be described in detail with reference to the accompanyingdrawings.

FIG. 1 is a constructional view illustrating an imaging lens accordingto an exemplary embodiment of the present invention.

The imaging lens comprised of a plurality of lenses is arranged about anoptical axis (ZO), a thickness, size, and shape of each lens are ratheroverdrawn in FIG. 1 for description, and a spherical shape or anaspheric shape has been only presented as one exemplary embodiment, butobviously not limited to this shape.

Referring to FIG. 1, a camera lens module according to the presentinvention includes, in an ordered way from an object side, a first lens(10), a second lens (20), a third lens (30), a fourth lens (40), a fifthlens (50), a filter (60) and a photo-detector (70).

Light corresponding to image information of a subject is incident on thephoto-detector (70) by passing the first lens (10), the second lens(20), the third lens (30), the fourth lens (40), the fifth lens (50) andthe filter (60).

The imaging lens according to the present invention includes five piecesof lenses including the first lens (10), the second lens (20), the thirdlens (30), the fourth lens (40) and the fifth lens (50), such that theimaging lens according to the present invention has an advantageouseffect in that flare can be reduced by interposing a separate aperturebetween a first lens and a second lens to correct aberration and torealize a clear image and by constructing the imaging lens with 5 piecesof lenses comprised of first, second, third, fourth and fifth lenses.

Hereinafter, in the description of the construction of each lens,“object side surface” means the surface of a lens facing an object sidewith respect to an optical axis, “image side surface” means the surfaceof the lens facing an imaging surface with respect to the optical axis,and upper side surface means the surface of the lens a capturing surfacewith respect to an optical axis.

In the specification, “imaging” basically may refer to the process inwhich an imaging lens receives light from a subject in the field andoutputs an image (image signal and image data) indicating the same.However, if the imaging lens is repeatedly generating the imageindicating the subject in the field at a predetermined cycle, “imaging”may mean the process of storing a specific image out of the imagesgenerated by the imaging lens in a storage unit. In other words, from acertain standpoint, “imaging” may mean a process in which the imaginglens acquires an image indicating the content of the subject in thefield and having the same in a state subjectable to the measurementprocess at a certain intended timing.

The first lens (10) has positive (+) refractive power, and is convexlyformed at an object side surface (S1). The second lens (20) has negative(−) refractive power, and is concavely formed at an upper side surface(S4). Furthermore, a separate aperture is interposed between the firstand second lenses (10, 20). In addition, the third and fourth lenses(30, 40) have positive (+) refractive power, and the fifth lens (50) hasnegative (−) refractive power. As illustrated, the third lens (30) takesa meniscus form convexly formed at an upper side surface (S6), thefourth lens (40) takes a meniscus form convexly formed at an upper sidesurface (S8), and the fifth lens (50) takes a meniscus form convexlyformed at an upper side surface (S19).

For information, ‘S2’ of FIG. 1 is an upper side surface of the firstlens (10), ‘S3’ is an object side surface of the second lens(20), ‘S5’is an upper side surface of the third lens(30), ‘S7 is an object sidesurface of the fourth lens(40), ‘S9’ is an object side surface of thefifth lens(50), and ‘S11’ and ‘S12’ are respectively object side surfaceand upper side surface of the filter (60).

Furthermore, one or more lenses of the first to fifth lenses (10, 20,30, 40, 50) may be formed with aspheric shape. The filter (60) may beany one optical filter selected from an infrared filter and a coverglass. The filter (60), if applied with the infrared filter, blocksradiant heat emitted from external light from being transferred to thephoto-detector (70). Furthermore, the infrared filter transmits visiblelight and reflects infrared rays to output it to the outside.

The photo-detector (70) is an image sensor, for example, CCD (ChargeCoupled Device) or CMOS (Complementary Metal Oxide Semiconductor), etc.

The first lens (10), the second lens (20), the third lens (30), thefourth lens (40) and the fifth lens (50) respectively use an asphericlens as later-described in the exemplary embodiments, to possiblyimprove resolution of a lens and have a good point of superioraberration property.

Furthermore, the imaging lens of the present invention is formed with anaperture interposed between the first lens (10) and the second lens (20)to reduce flare and determine a stable CRA (Chief Ray Angle) curve, andto realize a high picture quality when combined with a sensor.

Because the later-described conditional expressions and exemplaryembodiments are preferred embodiments enhancing an effect ofinteraction, it would be obvious to those skilled in the art that thepresent invention is not necessarily comprised of the followingconditions. For example, only by satisfying some conditions oflater-described conditional expressions, the lens construction(framework) of the present invention may have an enhanced effect ofinteraction.

0.5<fl/f<1.5  [Conditional expression 1]

0.5<ΣT/f<1.5  [Conditional expression 2]

1.6<N2<1.7  [Conditional expression 3]

20<V2<30  [Conditional expression 4]

50<V3, V4, V5<60  [Conditional expression 5]

where, f: an entire focus distance of the imaging lensfl: a focus distance of the first lensΣT: a distance from object side surface of the first lens to animage-forming surfaceN2: refractive index of second lensV2, V3, V4, V5: Abbe's numbers of the second to fifth lenses

Conditional expression 1 specifies refractive power of the first lens(10), The first lens (10) has refractive power having an appropriatecompensation of spherical aberration and appropriate chromaticaberration according to the conditional expression 1. The conditionalexpression 2 specifies dimension of optical axis direction of the entireoptical system, and it is a condition for ultra-small lens and acondition for appropriate aberration compensation.

Conditional expression 3 specifies refractive index of the second lens(20), conditional expression 4 specifies Abbe's number of second lens(20), and conditional expression 5 specifies Abbe's numbers of third,fourth and fifth lenses (30, 40, 50). The specification of Abbe's numberof each lens is a condition for better compensation of chromaticaberration.

Hereinafter, the action and effect of the present invention will bedescribed with reference to a specific exemplary embodiment. Asphericmentioned in a later-exemplary embodiment is obtained from a knownEquation 1, and ‘E and its succeeding number’ used in Conic constant kand aspheric coefficient A, B, C, D, E, F indicates 10's power. Forexample, E+01 denotes 10.sup.1, and E-02 denotes 10.sup.-2.

$\begin{matrix}{Z = {\frac{{cY}^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right)c^{2}Y^{2}}}} + {AY}^{4} + {BY}^{4} + {CY}^{4} + {DY}^{4} + {EY}^{4} + {FY}^{4} + \ldots}} & {\langle{{Equation}\mspace{14mu} 1}\rangle}\end{matrix}$

where, z: distance from the lens's top-point to an optical axisdirection, c: basic curvature of a lens, Y: distance towards a directionperpendicular to an optical axis, K: conic constant, and A, B, C, D, E,F: aspheric coefficients

EXEMPLARY EMBODIMENTS

The following Table 1 shows an exemplary embodiment matching theafore-mentioned conditional expressions.

TABLE 1 Exemplary embodiments f 4.13 f1 2.56 f2 −3.64 f3 9.73 f4 10.25f5 −5.79 |f2/f1| 1.42 ΣT 4.7 ΣT/f 1.138

Referring to Table 1, it can be noted that fl/f is 0.619 that matchesthe conditional expression 1, and ΣT/f is 1.138 that matches theconditional expression 2.

The following Table 2 shows an exemplary embodiment which is a moredetailed exemplary embodiment over that of Table 1.

TABLE 2 Surface Curvature radius Thickness or Refractive number (R)distance (d) index (N) materials  1* 1.45 0.54 1.54 Plastic  2* −30.90.01 (stop) 0.00 0.10  4* 4.81 0.28 1.64 Plastic  5* 1.53 0.39  6*−17.20 0.40 1.53 Plastic  7* −4.02 0.45  8* −1.48 0.40 1.59 Plastic  9*−1.31 0.10 10* 3.75 0.79 1.53 Plastic 11* 1.57 0.50 12 0.00 0.30 1.52IR-filter 13 0.00 0.49 image 0.00 0.00

The notation * in the above Table 2 and following Table 3, which isfurther written near the surface number indicates aspheric. Thefollowing Table 3 shows a value of aspheric coefficient of each lens inthe exemplary embodiment of Table 2.

TABLE 3 Surface number k A B C D 1* −0.017728 0.628476E−02 0.152202E−01−0.638397E−02 0.458047E−02 2* 0.000000 0.261702E−01 0.349096E−01−0.335264E−01 −0.456028E−02 4* −71.865663 −0.745618E−02 0.500326E−01−0.488897E−01 −0.673676E−03 5* −2.031149 −0.353626E−01 0.172119E+00−0.741018E−01 −0.251820E−01 6* 0.000000 −0.869724E−01 −0.724965E−020.311328E−01 0.176204E−01 7* 8.781701 −0.358819E−01 −0.331210E−020.147494E−01 0.945970E−02 8* −8.051573 −0.352205E−01 0.544751E−01−0.561835E−01 0.400188E−01 9* −2.070879 0.842341E−01 −0.501933E−010.308768E−01 −0.955785E−02 10* −65.990395 −0.101702E+00 0.234127E−01−0.248579E−02 −0.248383E−04 11* −10.265610 −0.683924E−01 0.176615E−01−0.555727E−02 0.864770E−03

MODE FOR THE INVENTION

FIG. 2, as a graph measuring coma aberration, is a graph illustratingcoma aberration according to an exemplary embodiment of the presentinvention, where tangential aberration and sagittal aberration of eachwavelength based on a field height are measured. In FIG. 2, it isinterpreted that a coma aberration correcting function is good as curvesapproach the X axis from a positive axis and a negative axis. In a shownaberration diagram, because values of images in nearly all fieldsproximate to the X axis, coma aberration correction functiondemonstrates a superior figure.

FIG. 3 is a graph illustrating spherical aberration according to anexemplary embodiment of the present invention. That is, FIG. 3 is agraph measuring longitudinal spherical aberration, astigmatic fieldcurves and distortion in order from left side. In FIG. 3, a Y axis meanssize of an image, and an X axis means focal distance (unit: mm) anddistortion degree (unit: %). In FIG. 3, it is interpreted that anaberration correcting function is good as curves approach the Y axis. Inthe shown aberration diagram, because values of images in nearly allfields appear proximate to the Y axis, longitudinal sphericalaberration, astigmatic field curves and distortion all demonstrate asuperior figure.

That is, a range of the longitudinal spherical aberration is −0.007mm˜+0.008 mm, a range of astigmatic field curves is −0.018 mm˜+0.004 mm,and a range of distortion is 0.00 mm˜+1.00 mm, such that the imaginglens according to the present invention can correct the characteristicsof longitudinal spherical aberration, astigmatic field curves anddistortion, whereby the imaging lens according to the present inventionhas an excellent lens characteristics.

The previous description of the present invention is provided to enableany person skilled in the art to make or use the invention. Variousmodifications to the invention will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother variations without departing from the spirit or scope of theinvention. Thus, the invention is not intended to limit the examplesdescribed herein, but is to be accorded the widest scope consistent withthe principles and novel features disclosed herein.

INDUSTRIAL APPLICABILITY

As apparent from the foregoing, the imaging lens according to theexemplary embodiments of the present invention has an industrialapplicability in that flare can be reduced by interposing a separateaperture between a first lens and a second lens to correct aberrationand to realize a clear image and by constructing the imaging lens with 5pieces of lenses comprised of first, second, third, fourth and fifthlenses.

1. An imaging lens, the imaging lens comprising, in an ordered way froman object side,: a first lens having positive (+) refractive power; asecond lens having negative (−) refractive power; a third lens havingpositive (+) refractive power; a fourth lens having positive (+)refractive power; and a fifth lens having negative (−) refractive power,wherein an aperture is interposed between the first and second lenses,and the imaging lens meets a conditional expression of 20<V2<30 and50<V3,V4,V5<60, where Abbe's number of second lens is V2, Abbe's numberof third lens is V3, Abbe's number of fourth lens is V4, and Abbe'snumber of fifth lens is V5.
 2. The imaging lens of claim 1, wherein anobject side surface of the first lens is convexly formed.
 3. The imaginglens of claim 1, wherein the second lens takes a concave form at anupper side surface.
 4. The imaging lens of claim 1, wherein the third,fourth and fifth lenses respectively take a meniscus form convexlyformed at an upper side surface.
 5. The imaging lens of claim 4, whereinany one lens or more lenses from the first, second, third, fourth andfifth lenses take an aspheric form.
 6. The imaging lens of claim 1,wherein the imaging lens meets a conditional expression of 0.5<fl/f<1.5,where f is an entire focus distance of the imaging lens, and fl is afocus distance of the first lens.
 7. The imaging lens of claim 1,wherein the imaging lens meets a conditional expression of 0.5<ΣT/f<1.5,where f is an entire focus distance of the imaging lens, and ET is adistance from an object side surface of the first lens to animage-forming surface.
 8. The imaging lens of claim 1, wherein theimaging lens meets a conditional expression of 1.6<N2<1.7, where N2 is arefractive index of the second lens.